The present invention relates to machine tools, and more particularly to machine tools having one or more work stations and a workpiece guiding and clamping system for moving the workpiece along axes of the machine relative to the work station(s).
Machine tools for performing various types of work upon flat sheet-like workpieces generally include at least one work station having a punching, nibbling, thermal cutting, routing, milling, drilling or like tool(s) to operate upon the workpiece. The workpiece guidance system generally includes a holding device which is movable in at least one direction relative to the work station. Such machine tools may comprise punching machines, nibbling machines, milling machines, plasma cutting machines, and laser cutting machines; routing, drilling or plasma or laser cutting stations may be provided as a second work station on a punching or nibbling machine, or as a separate machine.
The workpiece guidance system generally will include at least two clamping members and functions to move the workpiece during the machining operation relative to the stationary work station and in the plane of the workpiece. This movement or shifting of the workpiece is generally in the X and Y axes of a coordinate guide system, and may include superimposed motions running diagonally, or along an arc, or in a circle. Normally the workpiece comprises a sheet metal plate, and the workpiece holders grip or clamp one of the edges of the sheet metal plate.
As is well known, the machining of the workpiece will frequently be done up to, or nearly to, the edge of the workpiece. Under some circumstances, this can require release and resetting of the workpiece clamping members to permit the previously gripped portion to be advanced relative to the work station for working thereon; this may produce machining accuracies resulting from the releasing and regripping of the workpiece after movement of the clamping members or of the coordinate guidance system.
Moveover, relatively large workpieces vibrate substantially because the center of gravity of the workpiece is at a relatively large distance from the clamping devices. With such large workpieces, the clamping members of the guidance systems are subjected to a heavy loading during acceleration and deceleration in indexing of the workpiece.
It is an object of the present invention to provide a novel machine tool having an improved workpiece guidance system in which the machining of the workpiece in the edge area initially clamped for movement thereof about the machine tool is readily effected without introduction of errors resulting from repositioning of the clamping devices.
It is also an object to provide such a machine tool capable of reducing the load on its guidance assemblies during the acceleration and deceleration of the workpiece during its movement relative to the work station.
Another object is to provide such a machine tool in which the work stations and the working area of the machines may be better utilized to effect working upon substantially the entire surface area of a workpiece.